David Hodson, of the international cereal rust monitoring system at the UN Food and Agriculture Organisation, told a global wheat rust symposium in Minneapolis last week that Ug99 is now in Uganda, Kenya, Ethiopia, Sudan, Yemen, Iran, Tanzania, South Africa, Zimbabwe, Mozambique and Eritrea. Yemen is a particular concern as Ug99 is well-established and prevailing winds could carry the pathogen towards South Asia.
"Future spread of these variants is inevitable," says Hodson.
India, Pakistan, and even Australia and the Americas could eventually be hit.
Ronnie Coffman, who heads the durable rust resistance in wheat project at Cornell University which is co-ordinating the fight against the disease, says we are facing the "prospect of a biological firestorm".
"But it's also clear the research community has responded to the threat at top speed and we are getting results in the form of new varieties that are resistant to rust and appealing to farmers."
Work on breeding resistance to the rust started five years ago. The focus is on finding genetic resistance that can be transferred to local varieties, rather than creating a single variety which can withstand the disease.
More than 20 countries now contribute data to the Ug99 surveillance and monitoring system, compared to only two in 2007. Efforts are underway to add 10 more.
However, Coffman and his colleagues say significant obstacles still have to be overcome before new varieties can replace the susceptible wheats grown across about 225 million ha of South Asia, the Middle East, China, Europe, Australia and North America.
"Now it's a question of whether nations are willing to invest the political and economic capital necessary for agricultural research to secure the world's wheat supply."
Researchers at Penn State University and the U.S. Department of Agriculture (USDA) are adapting a system used to forecast soybean rust movements to track how Ug99 might travel from Africa by wind into wheat-growing regions of the US.
Wheat breeding expert Ravi Singh of the Mexico-based International Maize and Wheat Improvement Centre and colleagues from the Kenya Agricultural Research Institute, the Ethiopian Institute of Agricultural Research (EIAR) and the USDA, told the symposium new varieties under development have resistance to all three rusts of wheat: stem rust, yellow rust and leaf rust. Some new varieties yield 10% to 15% more than current cultivars.
"We have made tremendous progress on the science side, but now we need to see progress on the development side," Singh says. "Scientists can only do so much. We need to see national governments making the investments in seed systems development, including seed production and distribution. In many areas there will need to be support and leadership from wealthy countries and international institutions to carry these innovations into farmers' fields."